<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>验证用户名和密码</title>
</head>
<body>
    <script>
        var username = "admin";
        var password = "123456";
        var flag = false;
 
        while(flag === false) {
            var inputUsername = prompt("请输入用户名");
            var inputPassword = prompt("请输入密码");
            if (inputUsername === username && inputPassword === password) {
                alert("登录成功");
                flag = true;
            } else {
                alert("用户名或密码错误");
            }
        }
    </script>
</body>
</html>